Anti-corrosion cathodic protection devices having sacrificial anodes are known and widely used. Although such devices serve their intended purpose, anti-corrosion cathodic protection devices having sacrificial anode in the prior art exhibit some drawbacks.
Metal structures to be protected against corrosion, particularly maritime or nautical structures are generally placed in locations that can be hardly reached or that are difficult to reach due to the limited space available on boats.
In particular, the immersed portions of boats need to be protected against corrosion, for example, portions of the keel, propellers, the rudder and particularly transverse operating maneuvering propellers, so called bow thrusters.
Since propellers, particularly bow thrusters, are immersed in water for all the time the boat is on water, propellers must be provided with a level of corrosion protection that is effective, inexpensive and easy for maintenance. Typically, the protection employed is cathodic, wherein corrosion that may attack a structure attacks instead an anode, rather than attacking the structure. The anode is typically (but not exclusively) made of zinc, which, due to a known electrochemical reaction, is corroded instead of the structure to be protected. The anode is called “sacrificial anode” in jargon, since it is designed to be worn out because of the electrochemical reaction, preventing corrosion of the structure to which the anode is electrically connected thereto.
Once the sacrificial anode is worn out, it is replaced, protecting the structure from new corrosive attacks. The anode must be timely replaced, especially for immersed structures, such as propellers or the like, in order to prevent a corrosive attack on the structure, and a related weakening of the structure.
Consequently, the wear condition of the sacrificial anode must be verified periodically, in order to identify the wear state of the anode before the cathodic protection device stops operating due to dissolution of the anode.
An important drawback in addition to what described above is that the corrosion rate, and, therefore, the time needed for replacement, changes according to a number of elements, so it is necessary to frequently inspect or monitor the wear condition of the anode. Consequently, it is hardly possible to forecast when the anode will have to be replaced, but on the contrary the anode must be frequently inspected, or must be replaced before necessary.
Replacing the anode too early, that is, when it is not worn out yet, is not a preferred solution, since the anode is not completely used and costs are increased by replacing an anode that is still operating, even for a relatively short time.
Solutions in prior art have been provided for monitoring anode wear state, for example by measuring the electric current flowing in the anode by means of wires electrically connecting the anode to a measurement device.
Therefore, in order to have information about the state of anode wear state, either anode wear must be verified by visual inspection or a cable connection must be provided between the anode and the measurement device.
In general, but particularly for bow thrusters or maneuvering propellers, or more generally for the immersed structures of a boat, or for a fixed installation, inspection is often complex and also expensive. Trained personnel must dive and monitor the wear condition of the anode for ascertaining whether corrosion or wear has cause the anode to be replaced. This situation causes a considerable waste of time and money, and at the same time does not guarantee a timely replacement of the anode when it is corroded to the point that it can no longer perform its function. The owner of a boat or the captain must provide the time, equipment and knowledge necessary for diving and for checking the wear or use or corrosion conditions of the anode, or specialized personnel must be trained for such job, involving high costs.
On the contrary, if the condition of the anode is verified by using a cable monitoring system according to the prior art, for example by an electrical measurement, additional problems must be considered. For example, a wire must be provided, which contacts the marine or submarine environment, for connecting the anode with the measurement device. The cable, or wire, must be insulated from water, especially if the monitoring function requires the use of electricity, and the cable or wire itself is subjected to corrosion because of the marine environment, causing the wire to become worn, corroded or oxidized, so that it cannot appropriately carry out the monitoring function it has been designed for.
Moreover, monitoring through a cable requires that the operating conditions of the monitoring device be checked regularly, in order to insure proper operation. A malfunctioning of the monitoring device can cause no generation of a signal indicating a corroded anode, thus parts of the structure to be protected by the sacrificial anode become exposed to corrosion. As an alternative, the device monitoring the anode corrosion may indicate a malfunction, but this requires trained personnel to monitor and maintain the monitoring device, causing undesired costs and expenditures of time. On the other hand, it is well known that the marine environment attacks particularly immersed devices, and so a malfunction may be expected when using a cable, or a wire monitoring function.